Small & Blurry Hen Harrier

Sat editing photos, while watching "Homeland" on my iPad at the side of me, I suddenly noticed, out the window, out of the very corner of my eye a large white bird flying around against the brown rushes of the field.

I thought, that's not a seagull. What the heck is that?

This is a small and blurry photo, as I watched it for about 5 minutes, before the OH came in and I had a chance to shout "Bring the camera! Quick!!"

I only had my 70-200mm lens on the end of he 20D. Out of my attic window, in the field across the road, so a fair distance away.

It was flying around nicely, swooping, then rising, briefly perching on a tree, then off again.

Then a great big bully of a buzzard came along and swooped down at it!
Off it went over the top of the house and away.

I think it's a Hen Harrier (Circus cyaneus). If I'm wrong (I'm not a full time twitcher) please let me know.